Declarative Programming using Nested Structures¶
In this chapter we are going to learn how to build declarative programming world using nested structures on the top of object oriented.
We will learn about
Creating Objects inside Lists
Composition and Returning Objects and Lists by Reference
Executing code after the end of object access
Declarative Programming on the top of Object-Oriented
Creating Objects inside Lists¶
We can create objects inside lists during list definition. Also we can add objects to the list at any time using the Add() function or the + operator.
Example:
alist = [new point, new point, new point] # create list contains three objects
alist + [1,2,3] # add another item to the list
see "Item 4 is a list contains 3 items" + nl
see alist[4]
add(alist , new point)
alist + new point
alist[5] { x = 100 y = 200 z = 300 }
alist[6] { x = 50 y = 150 z = 250 }
see "Object inside item 5" + nl
see alist[5]
see "Object inside item 6" + nl
see alist[6]
class point x y z
Output:
Item 4 is a list contains 3 items
1
2
3
Object inside item 5
x: 100.000000
y: 200.000000
z: 300.000000
Object inside item 6
x: 50.000000
y: 150.000000
z: 250.000000
Composition and Returning Objects and Lists by Reference¶
When we use composition and have object as one of the class attributes, when we return that object it will be returned by reference.
if the caller used the assignment operator, another copy of the object will be created.
The caller can avoid using the assignment operator and use the returned reference directly to access the object.
The same is done also if the attribute is a list (not object).
Note
Objects and Lists are treated using the same rules. When you pass them to function they are passed by reference, when you return them from functions they are returned by value except if it’s an object attribute where a return by reference will be done.
Example:
o1 = new Container
myobj = o1.addobj() # the assignment will create another copy
myobj.x = 100
myobj.y = 200
myobj.z = 300
see o1.aobjs[1] # print the object inside the container
see myobj # print the copy
Class Container
aObjs = []
func addobj
aobjs + new point
return aobjs[len(aobjs)] # return object by reference
Class point
x = 10
y = 20
z = 30
Output:
x: 10.000000
y: 20.000000
z: 30.000000
x: 100.000000
y: 200.000000
z: 300.000000
Example(2):
func main
o1 = new screen {
content[point()] {
x = 100
y = 200
z = 300
}
content[point()] {
x = 50
y = 150
z = 250
}
}
see o1.content[1]
see o1.content[2]
Class Screen
content = []
func point
content + new point
return len(content)
Class point
x = 10
y = 20
z = 30
Output:
x: 100.000000
y: 200.000000
z: 300.000000
x: 50.000000
y: 150.000000
z: 250.000000
Example(3):
func main
o1 = New Screen {
point() { # access the object using reference
x = 100
y = 200
z = 300
}
point() { # access the object using reference
x = 50
y = 150
z = 250
}
}
see o1.content[1]
see o1.content[2]
Class Screen
content = []
func point
content + new point
return content[len(content)] # return the object by reference
Class point x=10 y=20 z=30
Output:
x: 100.000000
y: 200.000000
z: 300.000000
x: 50.000000
y: 150.000000
z: 250.000000
Executing code after the end of object access¶
We can access an object using { } to use object attributes and methods.
if the object contains a method called BraceEnd(), it will be executed before the end of the object access.
Example:
New Point { See "How are you?" + nl }
Class Point x y z
func braceend
see "I'm fine, Thank you!" + nl
Output:
How are you?
I'm fine, Thank you!
Declarative Programming on the top of Object-Oriented¶
The next features enable us to build and use declarative programming environment using nested structures on the top of object oriented
using {} to access the object attributes and methods
BraceEnd() Method
returning objects by reference
Setter/Getter Methods (optional)
Example:
# Declarative Programming (Nested Structures)
Screen()
{
point()
{
x = 100
y = 200
z = 300
}
point()
{
x = 50
y = 150
z = 250
}
}
# Functions and Classes
Func screen return new screen
Class Screen
content = []
func point
content + new point
return content[len(content)]
func braceend
see "I have " + len(content) + " points!"
Class point
x=10 y=20 z=30
func braceend
see self
Output:
x: 100.000000
y: 200.000000
z: 300.000000
x: 50.000000
y: 150.000000
z: 250.000000
I have 2 points!
More Beautiful Code¶
We can get better results and a more beautiful code when we can avoid writing () after the method name when the methods doesn’t take parameters. This feature is not provided directly by the Ring language because there is a difference between object methods and object attributes. We can get a similar effect on the syntax of the code when we define a getter method for the object attribute. For example instead of defining the point() method. we will define the point attribute then the getpoint() method that will be executed once you try to get the value of the point attribute. since we write the variable name directly without () we can write point instead of point() and the method getpoint() will create the object and return the object reference for us.
Example:
new Container
{
Point
{
x=10
y=20
z=30
}
}
Class Container
aObjs = []
point
func getpoint
aObjs + new Point
return aObjs[len(aObjs)]
Class Point x y z
func braceend
see "3D Point" + nl + x + nl + y + nl + z + nl
Output
3D Point
10
20
30